High-throughput lithography and surface patterning with extremely fine linewidths (e.g., on the order of 10-100 nm) are important for future growth of the microelectronics industry and nanotechnology. However, the resolution of conventional projection optical lithographic systems, still the most widely used in the microelectronics industry, is limited by optical diffraction. While the resolution can be improved by using beam-based direct-writing tools with high energy and short wavelengths, such systems are complex and expensive, typically result in low throughput, and are not capable of depositing patterns made of biological molecules or chemical compounds (though special chemical resists can be used).
It has been discovered that scanning probe microscopy (SPM) probes can be used in nanolithography to produce patterns on surfaces of substrates. SPM probes include a probe tip attached to a suspension mechanism such as a cantilever. An exemplary SPM is an atomic force microscope (AFM). To produce a pattern, the SPM probe applies a patterning compound using the diffusion of a chemical or biological species from a tip of the probe to the surface. In a typical application, the patterning compound travels to the substrate via a meniscus that naturally forms between the tip and the substrate surface under ambient conditions.
This patterning method, generally referred to as Dip Pen Nanolithography (DPN), allows formation of microscale or nanoscale chemical patterns on surfaces using a microscopy probe such as that of an SPM. Such patterns may include, for example, linewidths on the order of 10 nm-100 nm or greater, and ultimate spatial resolution on the order of 5 nm. Features having linewidths in the 10 nm to several micrometer range, for example, can be fabricated using commercially available silicon nitride tips. An exemplary disclosure of a DPN method is contained in PCT/US-00/00319, which is incorporated herein by reference.
A brief description of an exemplary DPN process follows. As shown in FIG. 1, a tip 10 of a cantilevered probe such as an AFM probe is coated with a patterning compound 14, such as a chemical or a biological material, to be deposited on a surface of a substrate 16. The probe tip 10 is placed in contact with the surface. The patterning compound 14 is then free to diffuse from the probe tip 10 to the surface at the point of contact. Features may then be “drawn” on the surface of the substrate 16 by translating the probe tip 10, for example, along a writing direction W. As used herein, “in contact” means that the probe tip 10 is placed in sufficient proximity to the surface of the substrate 16 to permit transferring the patterning compound 14 to the surface by a method such as diffusion. The probe tip 10 may be scanned across the substrate surface, so that patterning compound 14 is transported through a meniscus 20 that forms between the probe tip and the surface. Once on the surface of the substrate 16, deposited molecules 18 anchor themselves to the substrate, forming robust patterns.
DPN offers a number of unique benefits, including direct writing capability, high resolution, ultrahigh nanostructure registration capabilities, and the flexibility to employ a variety of molecules for writing compounds (including biomolecules) and substrates (such as Au, SiO2, and GaAs). Other benefits include the ability to integrate multiple chemical, biochemical, or biological functionalities on a single “nano-chip”, a one-layer process for patterning, and the ability to automate patterning using customized software.
DPN technology can be implemented using a low-cost SPM instrument. In an exemplary setup, a DPN probe chip is mounted on an SPM scanner tube in a manner similar to commercially available SPM tips. Precise horizontal and vertical movement of a probe on the probe chip may be attained, for example, using an internal laser signal feedback control system of the SPM machine.
Multiple SPM probes can provide a throughput advantage for DPN over individual probes. For example, multiple probes may be arranged in one- or two-dimensional arrays in a probe chip, providing a plurality of probe tips in simultaneous contact with the surface.
Additional flexibility can be gained by providing actuators that allow individual probes to be independently addressable, most particularly when multiple probes are used, so that the probes can be selectively engaged with the substrate surface independently of other probes. Techniques for independently actuating one or more probes in a multiple-probe array are disclosed in related U.S. Pat. No. 6,642,129.